Conversion of an analog signal into a two-state signal is necessary before digital processing. For example, in automobile applications, a sensor coupled to a vehicle drivetrain provides an analog signal having a frequency related to vehicular speed. After conversion to a digital signal, a microcomputer detects the time interval of each cycle and computes vehicular speed by conventional algorithms.
It is known to provide a circuit for conditioning an input signal to a microcomputer utilizing hysteresis comparison. A circuit is provided for translating a signal into a two-state input signal for use by a microcomputer. The circuit comprises: summing means for adding electrical energy to the signal in response to a first feedback state of a feedback control signal to generate an intensified signal and for subtracting electrical energy from the signal in response to a second feedback state of the feedback control signal to generate a diminished signal. Controller means is coupled to the summing means for recognizing a first input state of the signal when the diminished signal exceeds a predetermined value and for recognizing a second input state of the signal when the intensified signal falls below the predetermined value. The controller means generate the feedback control signal, having the first feedback state when the diminished signal exceeds the predetermined value and having the second feedback state when the intensified signal falls below the predetermined value.
By subtracting electrical energy from the signal to generate a diminished signal, a relatively large positive excursion in the signal is required before a logic "1" is recognized. Similarly, by adding electrical power to generate an intensified signal after a logic "1" is recognized, a relatively large negative excursion in the signal is required before a logic "0" is recognized.
It is also known to use summing means for adding electrical energy to the signal in response to a first feedback state of a feedback control signal to generate an intensified signal and for subtracting electrical energy from the signal in response to a second feedback state of the feedback control signal to general a diminished signal. Switching means are responsive to the summing means for providing a negative edge interrupt signal when the diminished signal exceeds a predetermined value and for providing a positive edge interrupt signal when the intensified signal falls below the predetermined value. Microcomputer means are responsive to the switching means for generating the feedback control signal having the first feedback state in response to the negative edge interrupt signal and having the second feedback state in response to the positive edge interrupt signal. Preferably, after recognizing an interrupt transition, the microcomputer means disregard further changes in the interrupt signals until after generating the feedback output.
For some applications of this circuitry, there may be two or more types of analog to digital conversions needed if different sensors are employed to generate the analog signal, necessitating multiple hardware configurations, each adapted for a different conversion. Different electronic modules, then, containing the circuits would be needed. It would be desirable to achieve selective conversion of analog to digital signals without the need to have two different hardware configurations. More than one hardware configuration adds undesired cost and complexity for these converters.